The heart is a hollow muscular organ that contracts approx. 100,000 times a day and pumps approx. five liters of blood into the circulation every minute. It is not only characterized by the unique features of muscle tissue specialized to meet the constant physical demands of pumping blood, but also by muscle cells that send spontaneous rhythmic electrical impulses to stimulate contraction. This article gives an overview of the structure of the heart wall and of cardiac muscle tissue.

00:01
Well, let’s look at the
conducting system of the heart.
00:06
The conducting system of the heart consists
of the sinoatrial node, the atrioventricularnode, and then these bundles of conducting
fibres named in various ways, but I don’twant to get into those namings in this particular
lecture. In the middle section, labeled isthe atrioventricular bundle. It’s embedded
with connective tissue. It's cardiac musclecell. And on the right-hand side, you can
see the endocardium. And directly under theendocardium if you look very carefully, often,
you find evidence of these conducting fibrescalled Purkinje fibres. Now, the atrioventricular
bundle is just a large bundle of Purkinje fibres.
00:55
Those Purkinje fibres are then branched
out and head down through the myocardium,generally, very closely associated with the
subendocardial layer. And that’s whereyou could locate them histologically. Let
me stress that these conducting fibres ofthe heart are not nerves. They’re specialized
cardiac muscle. So if you look at the diagramof a heart, the blue circular structure
and the blue lines running down through themyocardium represents these conducting fibres.
And the white circular structure up at thetop that’s actually lying right next to
the entry of the superior vena cava isthe sinoatrial node. And it has processes
Purkinje fibres or conducing fibres radiatingfrom that sinoatrial node. The sinoatrial
node is the pacemaker of the heart.
02:04
Cardiac muscle, when it developed, has quite an inherent
ability to contract, that contracts withoutany stimulation except the impulses emanating
from the sinoatrial node. However, that sinoatrialnode can be influenced by the autonomic nervous
system. The firing rate of the impulse canbe increased or decreased by external factors,
not just nerves from the autonomic nervoussystem, but by other factors as well. So you
can increase or decrease the rate of the heartby influencing the rate of firing initiated
from that sinoatrial node. But essentially,those conducting fibres are cardiac muscle,
but they are just specialized. And you cantell the difference between these conducting
fibres from normal cardiac muscle. Have alook very carefully at the central section
of the atrioventricular bundle, or even havea look at the Purkinje fibres labeled just
under the endocardium. Both these labels orboth these fibres rather have clear types
of components within them. The cytoplasm isless duct stained, and sometimes, it’s even
very, very pale. That’s because these cardiacmuscles are conducting fibres. They’re not
contractile. So they don’t contain all thecontractile proteins, all the contractile
factory within the cell. They don’tneed it. So they don’t take up stain because
they’re not there. It’s as simple as that.
03:54
Another way you can tell the difference between
the Purkinje fibre, particularly, and surroundingcardiac muscle fibres is that Purkinje fibres
often have two nuclei. Remember, cardiac muscleonly has one nucleus.

About the Lecture

The lecture Conducting System of the Heart by Geoffrey Meyer, PhD is from the course Cardiovascular Histology.

Author of lecture Conducting System of the Heart

Geoffrey Meyer, PhD

Customer reviews

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Amazing

By Ammar T. on 30. December 2018 for Conducting System of the Heart

Thank you for all these amazing lectures and for making me love Histology.

VERY GOOD

By shelly g. on 08. December 2018 for Conducting System of the Heart

VERY WELL EXPLAINED VERY INFORMATIVE LOVED IT REALLY HELPED ME

I recommend

By Anastasia R. on 06. August 2018 for Conducting System of the Heart

Finally understood how the heart works! Great job at explaining :)

User Reviews

(3)
5,0 of 5 stars

5 Stars

3

4 Stars

0

3 Stars

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2 Stars

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1 Star

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Amazing

By Ammar T. on 30. December 2018 for Conducting System of the Heart

Thank you for all these amazing lectures and for making me love Histology.

VERY GOOD

By shelly g. on 08. December 2018 for Conducting System of the Heart

VERY WELL EXPLAINED VERY INFORMATIVE LOVED IT REALLY HELPED ME

I recommend

By Anastasia R. on 06. August 2018 for Conducting System of the Heart

Finally understood how the heart works! Great job at explaining :)

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